The invention is based on a priority application EP03293220.4 which is hereby incorporated by reference.
The invention relates to a method of evaluating a location of a mobile station within a cellular telecommunication network wherein a cell is associated with a base station, wherein the mobile station is located within the cell and wherein a timing advance is evaluated by the base station. The invention also relates to a corresponding base station and to a corresponding cellular telecommunication network.
A cellular telecommunication network, e.g. the Global System for Mobile Communication (GSM), is built up of a number of cells. The surface covered by all cells defines the operating area of the network. Each cell is associated with at least one base station. A mobile station being located within a specific cell, can therefore communicate with at least one base station belonging to this cell.
In connection with so-called location-based services, it is necessary to evaluate the actual location of a mobile station within the cell. For example, if all hotels in the vicinity of the actual location of a user of the mobile station shall be-provided to this user, the actual location of this user must be evaluated in order to carry out this location-based service.
It is known to evaluate the location of a mobile station within a cell as a function of a timing advance of the mobile station.
This timing advance is defined by each base station belonging to the cell and forwarded to the mobile station. The timing advance corresponds to that time duration which is required for sending data from the mobile station to the base station. In order to arrive at the base station at a predefined point in time, the mobile station must send its data prior to this point in time, i.e. with the given timing advance.
As described, the timing advance corresponds to the time duration required for transmitting data from the mobile station to the base station. The timing advance, therefore, depends on the distance of the mobile station to the base station. This results in the following known equation:rk=k×TA+offset  (equation A)with rk=distance from mobile station to base station,                k=constant value=e.g. 554 meters for GSM,        TA=0, 1, 2, . . . =timing advance,        offset=constant distance, e.g. k/2 or k/4.        
With the timing advance being evaluated by the base station as described above, the distance of the mobile station from the base station can be calculated with the above equation. Based on this distance, the location of the mobile station can then be evaluated and used in connection with location-based services.
However, the distance calculated with the above equation does not exactly correspond to the actual distance of the mobile station from the base station. This comes from the fact that the evaluation of the timing advance is not based on the shortest distance between the mobile station and the base station but on the actual transmission path between the mobile station and the base station including all diversions of the transmitted data due to reflexions and the like.
Therefore, the distance calculated with the above equation usually is longer than the actual distance between the mobile station and the base station.